1. Field of the Invention
The present invention relates generally to microwave ovens, and more particularly to a microwave oven control method and apparatus in which the humidity of air in a cooking cavity can be accurately detected without cooling the cooking cavity.
2. Description of the Related Art
In general, a microwave oven performs a cooking operation with the aid of a variety of sensors including environmental sensors, such as a humidity sensor, a temperature sensor and a gas sensor, and a weight sensor for detecting the weight of food.
The cooking operation is performed in such a way that a user selects a desired cooking item from an automatic cooking menu while food is laid on a turntable-type cooking tray in the cooking cavity of a microwave oven. In this case, the microprocessor of the microwave oven may receive the outputs of a humidity sensor, calculate a cooking time based on preset data and conditions, and control the operation of the magnetron of the microwave oven according to the result of the calculation.
In a conventional microwave oven control method, the lapse of a first cooking time is determined by calculating the slope of the output value curve of a sensor and determining whether the slope of the output value curve of the sensor is equal to a preset reference slope, a second cooking time is determined based on the first cooking time and a factor preset according to the kind of food, and a cooking operation is completed for the second cooking time.
However, in the conventional microwave oven method, while cooking operations are sequentially performed, current environmental conditions for temperature, humidity and gas sensors differ from those of a preceding cooking operation, so the slope of the output value curve of a sensor is changed, thereby making it difficult to determine the first cooking time. Accordingly, an initial waiting time of about twenty seconds should be set prior to starting a new cooking operation. That is, the magnetron is again operated after the magnetron has been stopped and the fan has been operated to cool the cooking cavity for the initial waiting time of about twenty seconds.
FIG. 1 is a graph explaining a conventional microwave oven control method.
Referring to FIG. 1, the cooling of a cooking cavity is performed for an initial waiting time TC of about twenty seconds at the first stage of a cooking operation. A first cooking time T1 is set as a period of time ranging from the end of the initial waiting time TC till the coincidence of the slope of the output value curve of the sensor with a preset reference slope A. Thereafter, a second cooking time T2 is set based on the first cooking time and a factor preset according to the kind of food. A cooking operation is completed for the second cooking time.
In one conventional system, the transition between the first cooking time T1 and the second cooking time T2 is based on an output of a humidity sensor, specifically a curve representative of the percentage of humidity detected over time. The conventional system determines when slope A has been met based on a detection of when a sampled humidity exceeds a predetermined amount. This predetermined amount had been determined, through experimentation, to typically be the point along the curve where an abrupt change occurs, ideally at the slope A position, for a particular food. However, such systems are very inaccurate as most real world foods do not match their ideal counterparts. Thus, a factory predetermined humidity level representative of an ideal point of abrupt change along such a curve will not typically match a real world point of abrupt change along a similar curve. In the conventional system, the actual slope of the curve is not detected, rather it is predicted that the abrupt change will occur at a certain sensor output, regardless of the actual slope of the curve. Therefore, an improved method and apparatus for actually detecting the approximate position of real world abrupt curve changes along an output sensor curve is necessary, rather than merely predicting where such abrupt curve change may occur.
In addition, as described above, in the conventional microwave oven, the cooling of the cooking cavity is performed by operating only a fan for the initial waiting time at the first stage of a cooking operation. Thus, because of the initial waiting time, the entire cooking time is lengthened and the power consumption of the microwave oven is increased. Even though the cooling of the cooking cavity is performed, an accurate control of the cooking operation becomes difficult because the control of the cooking operation is performed by detecting the slope of the output value curve of a sensor. Thus, a more accurate control of the cooking operation is needed.
Accordingly, to solve the above and other problems, an object of the present invention is to provide a microwave oven control method in which the humidity of air in a cooking cavity can be accurately detected without cooling the cooking cavity.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to accomplish the above objects, embodiments of the present invention provide a microwave oven control method and apparatus, the microwave oven including a magnetron generating high-frequency waves and a sensor detecting the environmental state of air in a cooking cavity, including: a first cooking period calculating step of sampling the outputs of the sensor at preset periods and calculating a first cooking period based on the result of the sampling; a second cooking period calculating step of calculating a second cooking time based on the first cooking time and the kind of food; and a cooking step of completing a cooking operation for the second cooking time.